1. Field of the Invention
The invention relates to a device for optically scanning a document, which device comprises a light source for illuminating the document to be scanned, an optical detection system and an optical fiber bundle for transmitting light from the light source to the document and for transmitting light from the document to the detection system, said fiber bundle comprising a plurality of optical fibers having a core and a cladding and each having a first and a second end, said first ends being arranged substantially along a line in a first end face of the fiber bundle and the second ends being arranged in a second end face, the second end face facing the light source and the detection system.
2. Description of the Related Art
A device of the type referred to above is used, for example, in a facsimile apparatus with which picture material can be transmitted electronically. Such a scanning device can also be used for storing copies of documents in electronic filing systems such as magnetic or optical memories and for processing text or picture documents by means of a computer.
A device as described in the opening paragraph is known from U.S. Pat. No. 4,570,063. In the device described in this patent the radiation beam generated by the light source is obliquely incident on the second end face of the fiber bundle. This results in a large part of the light incident on the second end face being reflected. A small part of the reflected light subsequently reaches the light-sensitive surface of the detection system directly, or after reflection on other parts of the scanning device. Of the light which is passed through the fiber bundle in the direction of the document a portion is reflected after Fresnel reflection on the fiber-air interface of the first end face and passed to the detection system via the fibers. Both these contributions result in a disturbing signal on the detection system. It has been found that these unwanted reflections throw a quantity of scattered light on the detection system, which quantity is larger than the signal light if no appropriate measures are taken. This is because only a few percent of the light incident via the fiber bundle on the document and being scattered on this document are captured within the numerical aperture of the fiber so that this light is passed to the detection system. The light incident on the detection system and originating from the document is thus only a very small portion of the total quantity of light emitted by the light source.